Preparation of dyes which contain sulfonic acid groups and have a low electrolyte content

Abstract

A process for the preparation of dyes which contain sulfonic acid groups and have a low electrolyte content, wherein an aqueous solution or suspension, which may or may not contain inorganic salts, of the dye containing sulfonic acid groups is (a) mixed with an amount, equivalent to the said dye, of a non-emulsifying, water-insoluble amine of a total of 12 to 40 carbon atoms, which forms, with the said dye, a salt which is sufficiently lipophilic for it to separate spontaneously from the aqueous phase, (b) the pH is brought to <5 with an acid and the batch is mixed thoroughly, (c) the two resulting phases of different density are separated, and (d) the phase which consists of the lipophilic ammonium salt of the dye is mixed, with or without prior washing with water, with a water-soluble base whose sulfonate salt is to be prepared, and with water, the resulting phases are separated, and the salt is left in the aqueous solution or is isolated therefrom.

We claim: 
     
       1. A process for the preparation of concentrated aqueous fluid formulation of dyes which contain sulfonic acid groups and have a low electrolyte content, wherein an aqueous solution or suspension, which may or may not contain inorganic salts, of the dye containing sulfonic acid groups is, in the absence of solvent (a) mixed, at elevated temperature above 50° C., with an amount, approximately stoichiometrically to the sulfo groups of the dye, of a non-emulsifying, water-insoluble amine of a total of 12 to 40 carbon atoms, which forms, with the said dye, a liquid salt which is sufficiently lipophilic that it separates from the aqueous phase,   (b) the pH is brought to <3 with an acid and the batch is mixed thoroughly,   (c) the two resulting phases of different density are separated, and   (d) the phase which consists of the lipophilic ammonium salt of the dye is mixed, with or without prior washing with water, with a water-soluble base whose sulfonate salt is to be prepared, and with water, the resulting phases are mechanically separated, and the salt is left in the aqueous solution or is isolated therefrom.   
     
     
       2. A process as claimed in claim 1, wherein the acid used is an inorganic acid, or formic acid. 
     
     
       3. A process as claimed in claim 1, wherein a secondary or tertiary amine is used as the amine in stage (a). 
     
     
       4. A process as claimed in claim 1, wherein a water-soluble amine is used as the base in stage (d). 
     
     
       5. A process as claimed in claim 1 or 4, wherein an alkanolamine is used as the water-soluble base.